1. Field of the Invention
The present invention relates to a hydraulic reservoir and, more particularly, to a hydraulic reservoir with an integral filter bowl formed by rotational molding.
2. Brief Description of the Prior Art
Rotational molding, or rotomolding, is a well-known method of forming objects from a plastic resin. It is often used for complex shapes including tanks and reservoirs. Various types of plastic resin can be used, such as polyethylenes, plastisols, nylons, fluoropolymers, polypropylenes, polyurethanes, and other suitable materials.
In general, a mold is loaded with a plastic resin and heated in an oven. As the mold is heated, the mold is rotated about two or even three, axes at a low speed. The heat melts the plastic resin inside the mold and melted resin coats the interior surface of the mold. The mold is then gradually cooled using air or water and the re-solidified plastic resin, which has assumed the shape of the interior walls of the mold, is removed from the mold. This process differs from injection molding in that the plastic resin is not pressurized (other than atmospheric pressure).
As shown in U.S. Pat. No. 5,285,923, it is occasionally necessary to insert objects made of a material other than plastic resin into the object to be formed, such as brass inserts molded into a polyethylene material. In general, the insert is placed in a designated spot in the mold, the plastic resin is added to the mold, and the rotomolding process is initiated as described above. The melted plastic resin encapsulates the insert and the insert becomes part of the finished product.
A problem associated with incorporating non-plastic materials into the plastic resin is that the expansion and contraction properties of the resin and the inserted objects are not necessarily equal and, therefore, leaks or gaps can develop between the inserted object and the cooled plastic resin. This problem is amplified by the fact that plastic resin is known to shrink an appreciable amount as it cools. U.S. Pat. Nos. 3,364,292; 4,023,257; 4,143,193; 4,847,028; and 5,911,938 also discuss rotomolding with inserts added to the molded product. All of the above-cited references are incorporated herein by reference.
As noted in the above-cited prior art, rotomolding is well-suited for forming a plastic tank or reservoir structure. Such tanks are often used as hydraulic reservoirs for hydraulic systems, such as used in heavy machinery, including cranes, backhoes, demolition shears, bulldozers, and the like. In hydraulic systems, it is important to keep the hydraulic fluid free of debris. Consequently, filtering elements have been incorporated in the hydraulic systems to filter debris from the hydraulic fluid.
It is an object of the present invention to provide a rotomolded hydraulic reservoir with an integral filter bowl. It is a further object of the present invention to provide a rotomolded hydraulic reservoir with integral filter bowl having an extended depth integral filter enclosure with a coupling insert. It is another object of the present invention to provide a rotomolded hydraulic reservoir with an improved baffle and a second fluid return. It is another object of the present invention to provide a hydraulic reservoir that is economically manufactured. It is a further object of the present invention to provide an effective, easily replaceable filter element for a hydraulic reservoir.
The above objects are achieved with a rotomolded hydraulic reservoir having an integral filter bowl according to the present invention. The hydraulic reservoir is a one-piece tank structure. Specifically, the hydraulic reservoir includes a plastic container body defining a container cavity for receiving the hydraulic fluid. The container body forms a filter cavity in fluid communication with the container cavity. A filter element coupling mechanism is provided in the filter cavity. The filter element coupling mechanism may be a coupling insert, such as a machined metallic bushing, which is molded in the container body adjacent the filter cavity. The filter element coupling mechanism defines an opening, such as the insert with an internal bore, providing the communication between the container cavity and the filter cavity. A removable filter element is positioned within the filter cavity and coupled to the filter element coupling mechanism. The removable filter element seals to the filter element coupling mechanism, such as the exterior of the insert.
In order to help ensure a positive seal between the resin and the insert to be included, the present invention generally may provide a container body forming a filter cavity with an end having, in cross section, a bowl-shape. The insert is positioned adjacent to the cross-sectional bowl-shape of the filter cavity. The bowl-shape offers controlled shrinkage tolerances in the general vicinity of the insert.
The present invention is particularly designed for rotomolding, however other molding or forming techniques are possible, such as blow molding, to form the present invention. A rotomolding method making the present invention is:
(a) positioning an insert into a mold configured to form a container body having a filter cavity with a bowl-shaped end;
(b) filling the mold with plastic resin;
(c) heating the resin while simultaneously rotating the mold about two axes; and
(d) cooling the mold.
The present invention provides a hydraulic reservoir with a filter wherein the incidence of leaks between the container and the filter element are minimized. The term hydraulic reservoir within the meaning of this application refers to a container for holding working fluid that is conveyed and returned to the reservoir in a circulating system or a holding container for fuel. Generally the working fluid in the circulating system is for hydraulic power or for lubrication, such as petroleum and water based fluids.
In one embodiment of the present invention, the fluid communication provided between the filter cavity and the container cavity is provided to extend to a level below the normal fluid level in the hydraulic reservoir to prevent foaming. Additionally, a second fluid return communicating with the container cavity may be provided in one embodiment of the present invention with the second fluid return including an integral metal coupling insert. The second fluid return may be provided with a fluid communication with the container cavity at a level lower than the normal fluid level within the container cavity. The normal fluid level for a hydraulic reservoir varies between rest and operating conditions. Although the normal fluid level is dynamic, the term normal fluid level is a specific defined range in a given reservoir and a given application.
One embodiment of the present invention includes a solid integral baffle formed in the rotomolded reservoir of the present invention. The solid integrally molded baffle extends from the bottom and only one side of the container cavity to about one-half of the container cavity and substantially the entire width of the container cavity. A gap is provided between the other side and the baffle with the gap extending to the bottom whereby fluid at any level within the container cavity can flow around the integral baffle. A baffle is a term referring to a structure within a container which is designed to control and optimize the fluid flow pattern within the container to provide deaeration and fluid and thermal homogenization to the fluid.
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout.